(a) Field of the invention
The present invention relates to a fuel supply device for internal combustion engines having an air supply quantity controlling system so formed that an air flow quantity to be supplied to an internal combustion engine is able to be controlled by an actuator operated with a computer.
(b) Description of the prior art
The air supply into an internal combustion engine for automobiles and the like is conventionally controlled by opening or shutting a throttle valve mechanically connected to an accelerator pedal through a movement transmitting mechanism by a driver depressing the accelerator pedal. By opening or shutting the throttle valve with an actuator of the electric, pneumatic, oil pressure or similar type, it is also thought to electrically detect the motion of the accelerator pedal, to calculate and process this detection signal by an electronic control unit such as a computer and the like, taking the operating state of the engine into consideration and to operate the actuator so as to be able to obtain an air flow quantity necessary for the internal combustion engine. By this sort of controlling mechanism, it is partly practised to hold the revolution speed constant in the idling operation and to the hold air-fuel ratio (A/F value) constant. Furthermore, it has been attempted to similarly control the air flow quantity in all operating conditions. However, in a fuel supply device of known air supply quantity controlling system, the air flow quantity passing the throttle valve provided with an actuator is able to be calculated and controlled with an air detecting means (for example, an air flow sensor) or with the actually measured value of air quantity according to the operating conditions of an internal combustion engine. By the way, the air flow sensor for automobiles has such inclination that the manufacturing is difficult and the formation is complicated because a high measuring accuracy is requested and, therefore, has such problems that the manufacturing cost increases, the responsiveness deteriorates because it is separately arranged from the engine body as it is easily under the influence of the intake system of the engine, a pressure loss is caused because it acts as a resistance in the air flow path, a large space is occupied by it and an increase of the weight of an automobile is introduced. On the other hand, in a system to determine an air flow quantity referring to an actually measured value from the operating condition of the internal combustion engine, for example from the intake manifold pressure and the number of revolutions of the engine, the air flow sensor having various defects as mentioned above is not needed. It is, however, difficult to adjust the air flow quantity so as to always maintain high accuracy because the influence of the irregularity of the properties of the engine and the change along the progress of time are large. Further, it is extremely problematic in practice that a great amount of the actually measured data is needed to be accumulated and controlled in accordance with the properties set up according to the kind and purpose of the engine. Furthermore, in the adjustment of air quantity at the A/F control, as the opening degree of the throttle valve is increased or decreased by a servomechanism so that the output value from the exhaust gas sensor is to be a desired value, it is not necessary to detect the adjusted quantity of air. This is, however, essentially different from the control of air quantity for controlling the engine output since the quantity of air to be adjusted is small and it brings forth no change to the engine of such a degree that a driver is able to feel heat.